A typical railcar has an elongated frame and a pair of wheeled truck assemblies attached to the frame. Each truck assembly is attached to the frame at each end of the railcar. Each wheeled truck assembly in turn includes flanged wheels that are adapted to roll on a pair of railroad track rails.
With the wheels on the railroad track rails, there may be clearance of only a few inches between the top of the rails and the underside of the railcar frame. Routine maintenance may require that the railcar frame be elevated somewhat in order to increase this clearance so that the underside of the frame may be serviced. One form of maintenance may require that the railcar be completely removed from one of the truck assemblies, to allow such truck assembly to be replaced or serviced. For example, to remove the assembly, the one end of the railcar may be lifted vertically about 10-30 inches, while the other end of the railcar remains supported on the other wheeled truck assembly. With the one railcar end so elevated, both old and new truck assemblies can be rolled along the rails.
One way of lifting one end of the railcar is by means of a crane. This is done by connecting the lift line of the crane to the railcar frame, such as at the railcar coupling. This requires the presence of a high capacity crane that can carry the load of the railcar, and such a crane will typically be quite large and represent a significant capital investment. Moreover, such a crane may be mounted on a special railroad service railcar or road vehicle. If the crane is limited to rolling along on track rails, it may not be conveniently moved from one site to another. If the crane is on a road vehicle, the crane may be used only at certain rail sites because of its size.
Another way the railcar can be removed from the wheeled truck assembly is by means of a pair of separate lift jacks, interposed between the underlying rail bed and each side of the railcar frame. These jacks are relatively inexpensive and quite portable. However, as the separate jacks bear against the rail bed, special shoring efforts may be needed in order to provide added stability to the jacks and to prevent the jacks from sinking into the rail bed. Moreover, with the jacks on opposite sides of the railcar, several people may be needed to operate the jacks.
One example of a railcar jack assembly is described in U.S. patent application Ser. No. 10/404,001, entitled “Center Sill Car Jack Utilizing Air Bellows” filed on Mar. 31, 2003. The jack assembly in such application incorporates a set of bellows to raise a car-engaging means that, in turn, lifts the railcar above a wheeled truck assembly.
Moreover, there are certain inherent risks with the use of either the crane or paired lift jacks because they bear the entire load of the railcar during the time the wheeled truck is removed from the railcar or while someone is under the railcar for servicing. A crosswind may cause the crane-suspended railcar to sway, or the paired jack-supported railcar may topple sideways off of the jacks. This can be both dangerous to personnel and destructive to property. Dangerously, any failure of the crane lift line or of either jack can allow the raised railcar to fall.